X-ray system with aligned source and slits

ABSTRACT

An X-ray system for producing a fan-shaped beam and scanning the beam over the object to be X-rayed for reducing fogging due to scattering and reducing exposure of the patient. A cassette for holding the record medium in a gas filled gap between electrodes, and a mechanism for rotating the record medium past a slit in synchronism with the X-ray beam scan.

United States Patent 1 1 [ll] 3,832,546 Morsell et al. Aug. 27, 1974 [5X-RAY SYSTEM WITH ALIGNED SOURCE 2,692,948 10/1954 Lion 250/3152,934,649 4/1960 ,Walkup 250/325 AND SLITS 3,536,913 10/1970 Huchel250/490 [75] Inventors: Arthur Lee Morsell, Tarzana; 3, 4 ,351 7 211972.la ry i s 250/325 Norton L. Moise, Los Angeles, both of Calif. PnmaryExaminer-James W. Lawrence [73] Asslgnee: Xomm, Inc-7 Van EW Cahf-Assistant ExaminerB. C. Anderson [22] Filed; Mar. 7, 1973 Attorney,Agent, or Firm-Harris, Kern, Wallen &

Tinsle 21 Appl. No.2 338,763 y Related US. Application Data v [62]Division of $61. No. 243,982, April 14, 1972, Pat. I ABS RACT An X-raysystem for producing a fan-shaped beam and 52 US. Cl. 250/315, 250/491Scanning the beam Over the Object to b y for 51 Im. c1 HOSg 1/00reducing fogging due to Scattering and reducing P [58] Field of Search250/315, 325, 490, 475, Sure f the Patient A Cassette for holding therecord 5 355/3 medium in a gas filled gap between electrodes, and amechanism for rotating the record medium past a slit 56] ReferencesCited I in synchronism with the X-ray beam scan.

UNITED STATES PATENTS 4 Chins, 7 Drawing Figures 2,624,652 l/l953Carlson 25/315 ill] X-RAY SYSTEM WITH ALIGNED SOURCE AND SLITS I This isa division of application Ser. No. 243,982, filed Apr. 14, 1972 now US.Pat. No. 3,766,315.

This invention relates to X-ray systems and, in particular to a new andimproved X-ray system which provides for scanning a narrow beam acrossthe object being X-rayed and a cassette for holding the record medium.The invention may be used with various known X-ray techniques and isparticularly adapted for use with radiographic systems in which X-raysource produces electrons to form an alectrostatic image suitable forprinting. This type of radiographic system is sometimes referred to asionography and utilizes a dielectric sheet as the recordmedium in placeof the more conventional photographic film. The variation in X-rayintensity exiting from the object illuminated by the X-ray sourceproduces a variation in electron density on the dielectric sheet. Theelectrostatic image on the dielectric sheet is then converted to avisual image using conventional techniques, such as the xerographicprocess. For further information on the basic ionographic system,referencemay be made to copending application entitled RADIOGRAPHICSYSTEM WITH XERO- GRAPHIC PRINTING, Ser. No. 217,394, filed Jan. 12,1972 and assigned to the same assignee as the present application. Thepresent application is directed to an improvement on the system of saidcopending application.

The ionographic system utilizes electrode with a gas at high pressure inthe gap between the electrodes. It is difficult to build a structurestrong enough to contain the high pressure gas and maintain theelectrode spacing, but still thin enough to permit the passage of X-rayradiation into the gap. This structural problem is.espe cially severe inthe case of devices with flat, large area gaps such as is required forpresent day medical X-ray practice. Curving the X-ray window structureeases the problem of providing the necessary strength and transparencyto X rays but introduces a number of other problems. Curving the X-raywindow without curving the electrode gap generates the problem offinding a suitable filler material to interpose between the curvedwindow and the flat gas gap; such filler must be transparent to X rays,yet must withstand the high gas pressure. If the gas gap is curved tomatch the curvature of the window, the bounding surfaces of the gap willnot be nearly perpendicular to the propagation direction of the X raysand hence there will be a loss in image quality.

All X-ray imaging systems suffer to some extent from the problem offogging of the image from radiation scattered from the object beingX-rayed. The usual means of handling this problem is the Potter-Buckydiaphragm, which is a device consisting of a grid of flat lead stripsseparated by strips of material transparent to X-rays. The device isplaced between the object being X-rayed and the imaging system carryingthe record medium. The strips of the grid are oriented with respect tothe X-ray source in such a way that undeflected rays.

are more likely to pass between the lead strips than are the raysdeflected by scattering in the object. A mechanism is provided formoving the grid during the X-ray exposure to eliminate the shadow of thegrid in the resulting image. The moving grid is quite effective inremoving the image fogging, but there is an'appreciable loss of desired,undeflected rays. Therefore when a Potter-Bucky diaphragm is used it isnecessary to increase the dosage to the patient by as much as a factorof three.

The system of the present invention provides a solution to the problemsencountered in these prior art systems. The system of the inventionprovides for scanning the X rays over the object in a narrow beamdefined by moving slits. The system of moving slits minimizes the doseor exposure received by the patient while maintaining the X-rayintensity at the record medium. The moving slit system alsosubstantially reduces the undesirable scattered radiation reaching theimaging system with the record medium. A reduction in fogging of theimage'is obtained without any loss of the desired unscattered rays. ThePotter-Bucky diaphragm is not needed and the patient exposure issubstantially reduced.

A cassette is provided for the dielectric sheet which serves as therecord medium in the ionographic system and includes a pair ofelectrodes, at least one of which is cylindrical, with the gas gaptherebetween. The outer electrode may be a cylindrical sleeve with highstructural strength resulting from the small radius of curvature andhence may be quite thin or have a thin window section with low X-rayabsorption while maintaining structural integrity and gap dimensionalcontrol under high gas pressure. A mechanism is provided for rotatingthe record medium as the cassette is moved across the image area. A slitlimits the exposure to a portion of the gas gap with bounding surfacesnearly perpendicular to the direction of propagation of the X-rays.

It is an object of the invention to provide a new and improved X-raysystem with these features. Other objects, advantages, features andresults will more fully appear in the course of the followingdescription. The drawings merely show and the description merelydescribes preferred embodiments of the present invention which are givenby way of illustration or example.

In the drawings:

FIG. 1 is a side view of an Xray system incorporating the presentlypreferred embodiment of the invention;

FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is an enlarged sectional view taken along the line 33 of FIG. 1;

FIG. 4 is an enlarged sectional view taken along the line 4-4 of FIG. 1;and

FIGS. 5, 6 and 7 are views similar to that of FIG. 4 showing alternativeembodiments of the invention.

Referring to FIGS. 14, the X-ray system includes a housing 10 with anupright support 11. The object to be X-rayed may rest on the top of thehousing 10 or on a table or other support (not shown) positioned abovethe housing 10. An arm 13 is joumalled in the upper end 14 of thesupport 11. An X-ray tube 15 is carried on the arm 13, preferably withthe target 16, at which the X rays are generated, aligned with the pivotaxis 17 of the arm 13. A shield 20 is carried on the tube 15 forlimiting radiation from the tube to a fan-shaped beam 21 by means of aslit 22 at the lower end of the shield 20.

An electrode unit 30 is carried at the lower end 3l of the arm 13. Inthe preferred embodiment illustrated, a shaft 32 is joumalled in the armend 31, with a gear 33 carried on one end of the shaft 32. A drive motor34' is carried on the arm 13 with a gear 35 on the motor output shaftengaging the gear 33 for rotating theshaft 32.

A mechanism is provided for Coupling the shaft 32 to the housing so thatrotation of the shaft will move the arm 13 as well as rotate theelectrode unit 30. One end of a strap 40 is fixed to a rib 41 carried ona frame member 42 in the housing 10. The strap 40 is Wrapped onan'intermediate section 43 of the shaft 32 with the other end of thestrap fixed to the shaft as by a screw 44. Another strap 46 is wrappedon the intermediate section 43 in the opposite direction with one endfixed to the rib 41 and the other end fixed to the shaft 32. Withthis'arrangement rotation of the shaft 32 drives the lower end 31 of thearm 13 laterally as seen in FIG. 3 in an arcuate path about the pivotaxis 17. Preferably but not necessarily, the lower surface of the rib 41is an arcuate section about the axis 17 providing minimum stress on thearm. Various other drive arrangements will readily be apparent, such asa single strap looped around the shaft 32 and anchored at both ends tothe rib 41 or a shaft gear engaging a gear rack on the rib 41. I

The electrode unit includes an inner-electrode 50 and an outer electrode51. The electrodes are cylindrical and concentric with a gap 52therebetween. The outer electrode 51 may be carried on the shaft 32 atthe intermediate section 43, with an electrical insulating sleeve 53between the electrode and shaft. The inner electrode 50 may be a slidefit onto the end 54 of the shaft 32 and threadedly engageable with athreaded portion 55. A gasket 56 provides a pressure seal and electricalinsulation between the inner and outer electrodes. A flexible tube 57connected to the end of the electrode 50 provides for introducing gasunder pressure into the gap through a passage 58. A high voltage from apower supply 60 may be connected across the electrodes by connecting'oneterminalof the power supply to the inner electrode through system groundand connecting the other terminal of the power supply to the outerelectrode through a feedthrough terminal 61 and a flexible conductor 62.

A sleeve 65 of a material opaque to X rays is-carried on the arm 13 andsurrounds the electrode unit 30. The sleeve may be mounted on a boss 66projecting laterally from the arm 13 by ascrew 67. A slit 68 is providedin the sleeve 65, with the slit 68 in alignment with the slit 22, thetarget 16 and the axis of rotation 69 of the shaft 32. In the embodimentillustrated in FIGS. 1-4, the inner electrode 50 isthe anode, and areceptor or record medium in the form of a dielectric sheet 70 iswrapped on the inner electrode 50. Typically the sheet 70 may be dippedin a volatile conducting liquid such as alcohol and then wrapped on theelectrode, after which the electrode is threaded onto the shaft. Theouter electrode 51 is constructed of a material which is highlytransparent to X rays, typically beryllium. The operation of the systemin forming the electrostatic image on the sheet 70 is the same as in theaforementioned copending application. The slot 68 is made just largeenough to admit all of the radiation beam 21 to illuminate a rectangularsegment at the gap 52 and thus confine the radiation to that part of thegas gap bounded by electrode surfaces nearly perpendicular to thedirection of incidence of the X rays, since the resolution of the imgeis degraded as the gas gap tilts with rayed thereby substantiallyeliminating fogging without .motor 34 is energized, and the X-ray tubeis turned on.

The drive motor rotates the shaft 32 which in turn rotates the anodecarrying the dielectric sheet and also moves the arm 13. The X-ray beam21 defined by the slits is scanned over the object and the sheet isexposed as the'sheet rotates during the scanning. When the mechanism hasmoved to the opposite extreme, the drive motor, electrode power supplyand X-ray tube are shut off and the anode is removed for development ofthe visual image in the conventional manner.

The scanning with the narrow beam formed by the aligned slits, one aboveand one below the object being X-rayed, can be utilized with astationary record medium, such as a flat sheet, as well as with therotating cassette construction, to obtain the advantages of minimumpatient exposure and minimum fogging. This arrangement would be suitablewhere maintenance of a gap between electrodes is not a problem. Also, arotating anode moving across the zone being X-rayed with exposure of therecord medium limited by a slit can be utilized where total exposure tothe object is not a problem, while obtaining the structural advantagesof the concentric cylinders with the high pressure gas in the gap.

Various modes of construction for the electrode arrangement may beutilized, such as having the two electrodes assembled as a unitexternally of the housing with the unit mounted on the shaft 32. Also,the relationship of anode and cathode can be changed as desired. In FIG.5, the outer electrode is operated as the anode, with the dielectricsheet 70 carried thereon. Further, it should be noted that bothelectrodes do not have to-rotate, it merely being required that thedielectric sheet rotate for scanning the exposure over the entire sheet.One alternative embodiment with the inner electrode serving as the anodeand rotating while the outer electrode is fixed, as shown in FIG. 6. Theinner electrode 50 is insulated from the shaft 32 at end 54 by aninsulating sleeve 72. In this embodiment, the outer electrode 51 alsoserves as the shield 65. The slit 68 is closed by a window 76 ofmaterial highly transparent to X rays, typically beryllium. The innersurface of the outer electrode 51 may be lined withvan insulator 77everywhere but in the region of the slit 68. With this construction,only a small amount of the expensive beryllium is required. Theinsulator 77 reduces the likelihood of breakdown between the outerelectrode and the sheet 70 when the gas pressure is lowered just priorto opening the cassette. Also, the gas gap between the electrodes can bevery small everywhere except in the region of the slit 68 with a savingin the amount of gas utilized.

As another alternative configuration, in the arrangement of FIG. 5 withthe dielectric sheet on the outer electrode, the outer electrode couldrotate with the inner electrode stationary.

While the electrodes are generally cylindrical in configuration, bothelectrodes do not have to be complete cylinders. By way of example, inthe embodiment of F IG. 7, the sheet 70 is carried on the inner surfaceof the rotating outer electrode 51. Since the system is operative onlyin the portion of the gap 52 adjacent the slit 68, the other electrodeneed only be present at the area of the slit 68 as the sheet 70 isdriven thereby. Hence the inner electrode 50 may be a strip carried on astationary insulating sleeve 80. With this configuration, the gap 52 maybe made very small everywhere except in the region 81. The outer surfaceof the electrode 50' can be convex as in FIG. 5, or flat as shown inFIG. 7, or concave. With the flat and concave shapes, the size of thebeam as determined by the size of the slit 68 can be increased and theexposure time reduced while maintaining the same quality of image. Thisis possible because the field lines between the electrodes are morenearly parallel to the path of the X rays through the gap for thenon-parallel electrode configurations. Similarly, the window 76 in theembodiment of FIG. 6 may be flat or convex.

In the preceding discussion, the ionographic system has utilized theelectrons produced in the gap by the X rays, with the electrons beingattracted toward the anode and collected on the dielectric sheet. In analternative mode, the positive ions produced in the gap by the X raysand attracted toward the cathode, may be collected on a dielectric sheetat the cathode and converted to a visual image in the same manner. Ifdesired, dielectric sheets may be disposed at cathode and anode forobtaining two images at the same time.

Although exemplary embodiments of the invention have been disclosed anddiscussed, it will be understood that other applications of theinvention are possible and that the embodiments disclosed may besubjected to various changes, modifications and substitutions withoutnecessarily departing from the spirit of the invention. By way ofexample, while a pivoting arm 13 has been illustrated with arcuatemotion for the slits, a translating system with a linear motion for theslits can also be utilized. The only requirement is the X-ray source,the slits and the axis of rotation of the cassette carrying the recordmedium be maintained in alignment during the scanning.

We claim:

1. In a cassette for a radiographic system or the like, the combinationof:

a pair of electrodes comprising an anode and a cathode, at least one ofsaid electrodes being cylindrical;

means for mounting said electrodes in spaced relation with a gaptherebetween to form a unit having an axis of rotation;

a dielectric sheet carried in said gap on said one elec trode;

means for maintaining a gas in said gap;

means for connecting a high voltage electric power supply across saidelectrodes for attracting charged particles towards said one electrodefor deposit on said sheet to form a latent electrostatic image;

means for moving said unit along a path during an exposure;

means for rotating said sheet and one electrode about said axis as saidunit is moved;

an X-ray source;

first means defining a first slit;

second means defining a second slit; and

means for mounting said source and first slit on one side of a zonefor-an object to be X-rayed and for mounting said second slit and uniton the other side of the zone,

with said source, slits and unit aligned defining an -X-ray path fromthe source through the slits to the unit, the gas in the gap absorbingX-ray photons and emitting charged particles;

with said means for moving saidunit including means for scanning saidsource across the zone in synchronism with unit movement maintainingsaid source and slits in alignment.

2. A cassette as defined in claim 1 wherein said means for mounting saidsource and slits includes:

a fixed support; and

a moving arm carried on said support with said source, slits and unit onsaid arm in alignment with each other.

3. A cassette as defined in claim 2 including:

a drive motor mounted on said arm; and

means coupling said drive motor to said fixed support with said motorwhen energized driving said arm relative to said support.

4. A cassette as defined in claim 3 with said arm pivotally mounted onsaid support with said source at the pivot axis of said arm and withsaid slits and anode axis of rotation moving in arcuate paths inalignment with the arm pivot axis.

1. In a cassette for a radiographic system or the like, the combinationof: a pair of electrodes comprising an anode and a cathode, at least oneof said electrodes being cylindrical; means for mounting said electrodesin spaced relation with a gap therebetween to form a unit having an axisof rotation; a dielectric sheet carried in said gap on said oneelectrode; means for maintaining a gas in said gap; means for connectinga high voltage electric power supply across said electrodes forattracting charged particles towards said one electrode for deposit onsaid sheet to form a latent electrostatic image; means for moving saidunit along a path during an exposure; means for rotating said sheet andone electrode about said axis as said unit is moved; an X-ray source;first means defining a first slit; second means defining a second slit;and means for mounting said source and first slit on one side of a zonefor an object to be X-rayed and for mounting said second slit and uniton the other side of the zone, with said source, slits and unit aligneddefining an X-ray path from the source through the slits to the unit,the gas in the gap absorbing X-ray photons and emitting chargedparticles; with said means for moving said unit including means forscanning said source across the zone in synchronism with unit movementmaintaining said source and slits in alignment.
 2. A cassette as definedin claim 1 wherein said means for mounting said source and slitsincludes: a fixed support; and a moving arm carried on said support withsaid source, slits and unit on said arm in alignment with each other. 3.A cassette as defined in claim 2 including: a drive motor mounted onsaid arm; and means coupling said drive motor to said fixed support withsaid motor when energized driving said arm relative to said support. 4.A cassette as defined in claim 3 with said arm pivotally mounted on saidsupport with said source at the pivot axis of said arm and with saidslits and anode axis of rotation moving in arcuate paths in alignmentwith the arm pivot axis.